1. Field
The present invention relates to an infrared detector and more particularly to a technology for optimizing fixed pattern noise, 1/f noise, matching and self-heating effect compensation characteristics of a micro-bolometer in an infrared detector including a micro-bolometer array.
2. Description of Related Art
An infrared detector is generally classified into a thermal-based detector and a light-based detector which responds to far-infrared radiation. The thermal-based detector is able to implement an image system for generating a temperature image of an object by using a thermal sensor array. As described above, an apparatus for obtaining the temperature image of the object by collecting black body radiation energy radiated from the object is designated as a far-infrared thermal imaging system.
It has been known that the thermal-based detector includes a bolometer, a micro-bolometer, pyroelectricity, and thermofile. When far-infrared in a band of 8˜14 μm which is black body radiated from every object is collected on the micro-bolometer by means of a lens, the temperature of the micro-bolometer rises/falls, and as a result, the electrical resistance of the micro-bolometer is changed. Therefore, it becomes possible to image the temperature distribution of a scene of the captured object in a remote manner by measuring the electrical resistance value of an array of the micro-bolometer active cell, that is, a micro-bolometer array.
While the micro-bolometer array has generally a signal size according to the resistance change less than 0.1% caused by a thermal image, it has substrate temperature dependency, that is, the change amount of 2 to 3% of the signal size per one degree of the substrate temperature and has a so-called fixed pattern noise (FPN) according to process non-uniformity of several % and circuit mismatch of several %. Therefore, it is a big problem of how to remove the FPN much larger than the signal caused by the thermal image.
In addition to this, in order to obtain the result according to the temperature change of an electrical resistive element, it is required to measure current flowing through the electrical resistive element after applying a bias voltage to the electrical resistive element, or to measure voltage applied to both ends of the resistive element after applying current bias to the electrical resistive element. Here, the temperature of the electrical resistive element rises by joule-heating. Such a phenomenon is called self-heating. This should be corrected which is irrelevant to far-infrared radiation to be detected.
The 1/f noise that the electrical resistive element of the micro-bolometer has is an important factor determining the performance of the infrared detector. The 1/f noise is required to be reduced. Consequently, the micro-bolometer array becomes to have very big fixed pattern noise (FPN) caused by process/temperature/self-heating/1/f noise (PTSF) variation.
Accordingly, in the infrared detector including the micro-bolometer array, a variety of researches are being conducted to improve the infrared detection performance by reducing the FPN characteristics and 1/f noise characteristics and by compensating the self-heating effect.